The invention relates to a drive device having an actuating drive as well as a position detection device.
U.S. Pat. No. 5,240,296 discloses such a drive device, which in this case is in the form of a locking device for a door of a vehicle, in which case a moving element which is in the form of a lever can be moved to two positions by an actuating drive, and the lever can lock and unlock the locking device.
The position detection device is a potentiometer whose conductor tracks are printed on a printed circuit, in which case these conductor tracks are made contact with by wipers, which are attached to the lever. Depending on the position in which the lever is located, the xe2x80x9clockedxe2x80x9d or xe2x80x9cunlockedxe2x80x9d position is detected and, furthermore, the actuating drive is switched on and switched off as a function of the detected position.
The way in which the actuating drive operates and its actuation as well as the detection of the position of the moving element intrinsically works satisfactorily, so that the desired positions can be identified.
However, a major disadvantage in this case is that the position detection device is subjected to severe environmental conditions, such as those which occur in vehicles, and these (the following may be mentioned in this context: temperature fluctuations, moisture, dust and the like) can lead to the position detection device malfunctioning. Furthermore, a position detection device in the form of a potentiometer is subject to wear, which occurs particularly when used in vehicles where the locking device is operated very frequently. In this context, one could consider using appropriate materials which are not subject to such high wear; however, as a rule, these are costly and, in fact, cannot be used for cost reduction in large-scale production.
Furthermore, a position detection device in the form of a potentiometer has the disadvantage that contact resistances can occur at the junction point between the wiper and the conductor track, and these lead to corruption of the indicated position so that, the correct position is not always indicated reliably, even in this case. However, correct indication of position is, in fact, absolutely essential in the application of a locking device since, for example, the actuating drive and thus the entire locking device may be in the xe2x80x9clockedxe2x80x9d state while the position detection indicates xe2x80x9cunlockedxe2x80x9d so that the actuating drive would then not be actuated at all, since the position detection device indicates that the actuating drive is already in the xe2x80x9cunlockedxe2x80x9d position, and it would thus be possible to open the door.
The invention is thus based on the object of improving the drive device (mentioned initially) having an actuating drive and a position detection device, in such a manner that the described disadvantages are avoided, thus resulting in reliable operation with a very simple formation.
The invention provides that the position detection device has a magnet element which is fitted to the moving element, as well as a Hall element which is arranged in the vicinity of the magnet element, in which case the Hall element is integrated in an electronic module.
The position of the moving element is detected using the physical Hall effect, which is described briefly at the end.
Since the moving element and the position detection device now no longer touch one another, this position detection device operates without making contact and thus without wear, so that, in consequence, the function of the drive device works reliably throughout the entire intrinsic life or throughout the entire life of the object in which it is fitted (for example a vehicle). The design and assembly of the drive device according to the invention are particularly simple, since there is no need for any alignment between the magnet element and the Hall element and sufficiently accurate proximity is adequate to ensure operation of the position detection device. Furthermore, there is no need to fit conductor tracks on the printed circuit or for the presence of wipers and wiper supports of a potentiometer, which actually become particularly complex if it is necessary to monitor the position through a number of revolutions of the moving element.
In a development of the invention, the electronic module is in the form of an ASIC. The term ASIC means an electronic module which has been specified during production or by programming for its application and for the tasks in question. An ASIC includes input and output circuits, memory, processors, monitoring devices (for temperature, voltage, short circuit and the like), sensors (for example the Hall element) and so on. This has the advantage that an integrated module is provided in a very small space. Further advantages include the reduced rest-current consumption, since the only functions which are implemented are those which are required for the respective application, and thus reduced manufacturing costs as well. Testing of an ASIC is likewise simplified, since there is no need to test all the functions of a multifunctional chip which is normally used. One important factor is still very good copying protection, since it is not possible to see from the outside of the ASIC what components it contains and which functions it provides. The integration of the sensor thus provides a so-called active sensor, which provides a signal which has already been evaluated and may have been filtered, for further processing. Signal processing at the detection point also allows sensitive and small measurement variables to be detected, amplified and passed on after evaluation, so that the sensitivity to interference is in consequence reduced. This is particularly important for the application in vehicles since malfunctions are often caused by electromagnetic interference in this case.
In a development of the invention, the electronic module has an evaluation circuit for the output signals of the Hall element and/or an actuation circuit for producing actuation signals for the actuating drive. This increases the compactness of the design since the actuation circuit as well as the evaluation circuit are integrated in the electronic module. It is also advantageous that there is no need for any further wiring, since the electronic module can be arranged with its evaluation circuit and its actuation circuit in the physical vicinity not only of the moving element but also of the actuating drive. This results in a drive device having an integrated actuating drive and an integrated sensor system, in which case the only wiring which need be routed to this drive device is that for the power supply and, possibly, for other signals by means of which the actuating drive is intended to be actuated from the outside.
A further advantage for use of the electronic module within the drive device and for integration of the evaluation circuit and/or of the actuation circuit in the electronic module is that the connection between the evaluation circuit and the Hall element which supplies the output signal as a function of the position, as well as the connection between the actuation circuit and the actuating drive can be kept extremely short, so that there is no need for any measures which would be required to prevent disturbances from radiated interference. This avoids not only the shielding against electromagnetic interference radiation, but also improves the reliability of the overall drive device.
In a development of the invention, the electronic module is arranged on a printed circuit which, in particular, is in the form of a flexible printed circuit, in which case the printed circuit is inserted in a housing of the drive device.
This makes the device very easy to assemble since, on the one hand, the printed circuit can be prefabricated at least together with the electronic modules and, possibly, with further wiring and further modules in a first step, in which case, on the other hand, the moving element, the actuating drive and further functional elements of the drive device can be inserted into the housing at this stage, so that, once they have been inserted, it is only necessary to fit the printed circuit with the electronic module, and the assembly of the drive device is thus complete. This assembly process substantially simpler since there is no need for any accurate alignment between the moving element and the position detection device, although it is necessary to ensure that the electronic module is arranged with its Hall element in the vicinity of the magnet element, which is attached to the moving element. The printed circuit in the housing may be a discrete component while, in contrast, it is also feasible for the printed circuit to be inserted into the housing cover first and then to be fitted onto the housing, or else to be an integral component of the housing cover. In this case, one conceivable production process would be for the printed circuit together with the electronic module to be produced first of all and, after this, for at least these two components to be surrounded (extrusion coated) with plastic in the form of a housing cover, so that both the printed circuit and the electronic module with its Hall element are located under the plastic coating, such that they are completely protected. During the production of such a housing cover, which may also intrinsically relate to the housing itself, connecting means can also be provided, such as plugs or sockets or the like. In order, for example, to produce the connection between a plug and the electronic module, the latter need not necessarily be a printed circuit with conductor tracks on it so that, instead of this, all that is necessary is for it to be possible to produce the conductor tracks, for example in the form of stamped conductor tracks, in the plastic housing cover. A flexible printed circuit can be accommodated particularly well in housings of complex design and is particularly advantageous in applications which are subject to oscillations and vibration, since these can be absorbed better by a flexible printed circuit than by a rigid printed circuit.
Hybrid modules or so-called lead frames are available as alternatives to printed circuits. A hybrid module comprises an electronic circuit which includes a plurality of electronic components (resistors, capacitors, processors, sensors). Such a module can thus be wired up just for one specific application, and just has to be inserted into the housing and connected to its peripherals (in particular a power supply).
The term lead frame means a component which initially has an electrically non-conductive substrate, composed, in particular, of plastic. This substrate is in the form of a largely planar surface, but can be bent, kinked or formed in some other suitable way for matching to the installation location. Electrically conducted regions, in particular tracks, are inserted in the substrate and are composed, for example, of stamped sheet-metal parts. One possible way of producing a lead frame is to place the stamped sheet-metal parts in a mold, and to extrusion-coat them with plastic. At the points at which an electrical component is located on the substrate, the relevant electrically conductive regions are connected to the outside and make contact with the relevant component. Plugs or the like can also be formed integrally with the substrate, or are likewise made contact with as a separate component. Thus, once again, after the fitting of the lead frame, this results in an electronic module whose functionality can be checked before installation in the housing. Only functional modules are thus installed in the housing, so that one possible fault source after completion of the entire drive device is prevented.
In a development of the invention, the magnet element is arranged in a magnet element holder, which is attached to a shaft of the moving element. This has the advantage of simple assembly, so that all that is necessary is just to plug the magnet element onto the shaft by means of the magnet element holder, although other attachment options (for example bonding) are also conceivable. The use of the magnet element holder furthermore also has the advantage that tolerances, in particular in the axial direction, can be compensated for by means of this magnet element holder. In addition, one and the same magnet, in particular a permanent magnet, can be fitted via this magnet element holder to different shafts or other moving elements which have different geometric shapes. Conversely, it is, of course, also conceivable to use different magnets on one and the same moving element via the magnet element holder.
As has already been described initially, one particularly advantageous application of the device according to the invention is in a locking device, in particular for a vehicle, since the operating conditions here are severe, and can be eliminated by the use of a Hall element according to the invention. Although this field of application is regarded as being particularly preferred, it should also be mentioned that the invention is not limited to this field of application, and other applications of the drive device according to the invention are conceivable, without leaving the idea of the invention.